Photoconductive surfaces find widespread use in photocopiers where they are used in the image formation process. Zinc oxide is one of the materials used in the process. The zinc oxide surface in the copier is electrically charged and then exposed the light image of a page to be copied. The lighted areas of the image cause the surface to be conductive so that the charge can be drained away, but the dark areas hold their charge. The black powdered "toner" is then distributed on the surface and sticks to the charged areas. The black image is then transferred to another sheet of paper with the application of heat.